1. Field of the Invention
The present invention relates to valve arrangements for high voltage fuses.
2. Description of the Prior Art
High voltage fuses and particularly high voltage expulsion type fuses are well known to the art. For example, U.S. Pat. No. 3,267,235 -- Barta, 3,176,100 -- Barta, 3,575,683 -- Fahnoe all disclose various configurations of high voltage expulsion type fuses. Such fuses are often utilized outdoors on utility poles, and thus, are directly exposed to adverse weather conditions including rain, sleet, hail, and snow. Accordingly, such high voltage expulsion type fuses have typically been hermetically sealed to prevent the admittance of moisture into the interior of the fuse. It has been discovered that moisture on the inside of the fuse typically results in deterioration and corrosion of the internal components of the fuse. Thus, proper fuse operation can be affected. However, it has also been discovered that despite the best attempts to provide a reliable hermetically sealed fuse which will maintain its sealed relationship even after years of use, leaks often occur as a result of rough handling, thermal expansion of various dissimilar parts of the fuse, corrosion and exposure to adverse weather conditions. Once even the smallest of leaks develops in the fuse, a phenomenon called "pumping" results which causes the ingress of moisture into the interior of the fuse. Pumping results because of the well known physical relationship of pressure, volume, and temperature. Since the fuse has a constant interior volume, any change in the temperature of the air in that volume correspondingly results in a change in the pressure in the interior of the fuse. Thus, when the temperature of the fuse drops rapidly such as during a rainstorm, the interior pressure of the fuse tends to drop rapidly so that the interior pressure of the fuse may become less than atmospheric pressure thereby causing any moisture on the surface of the fuse to be sucked through any minor defect around the various hermetic seals of the fuse. Once moisture is pumped into the fuse, it is usually retained in the fuse for an extended period of time because there is no atmospheric venting to dry the interior of the fuse. Consequently, after a period of time there may be deterioration of the interior components of the fuse. Accordingly, it has been discovered that it would be an advantageous advance in the art of circuit interruption to provide a valve arrangement for a high voltage fuse which permits substantial atmospheric venting to the interior of the fuse when the atmospheric pressure is greater than the pressure on the interior of the fuse so that a pressure less than atmospheric pressure is never obtained in the fuse, while subsantially checking the exhaust of gases during interruption of lower currents.